Various medical procedures require that one or more medical fluids be injected into the patient. Medical imaging procedures oftentimes involve the injection of a contrast media into the patient, possibly along with saline or other fluids. Other medical procedures involve injecting one or more fluids into a patient for therapeutic purposes. Power injectors may be used for these types of applications.
A power injector generally includes what is commonly referred to as a powerhead. One or more syringes may be mounted to the powerhead in various manners (e.g., detachably; rear-loading; front-loading; side-loading). Each syringe typically includes what may be characterized as a syringe plunger, piston, or the like. Each such syringe plunger is designed to interface with (e.g., contact and/or temporarily interconnect with) an appropriate syringe plunger driver that is incorporated into the powerhead, such that operation of the syringe plunger driver axially advances the associated syringe plunger inside and relative to a barrel of the syringe. One typical syringe plunger driver is in the form of a ram that is mounted on a threaded lead or drive screw. Rotation of the drive screw in one rotational direction advances the associated ram in one axial direction, while rotation of the drive screw in the opposite rotational direction advances the associated ram in the opposite axial direction.
At least certain injection procedures will incorporate one or more pressure limits. A power injector may be configured to undertake one or more actions in response to a pressure limit having been met or exceeded. In many cases, a pressure of a fluid discharge from the power injector is monitored/determined, and is then compared with one or more pressure limits. The accurateness of the pressure value that is compared with a pressure limit will of course influence the accuracy of the power injectors pressure-monitoring capabilities.
Pressure in the syringe may be calculated by determining the force to push the plunger and dividing that force by the effective surface area of the syringe plunger. The force to push the plunger can be acquired by various methods, including direct reading from a load-cell or the like or a drive motor power calculation using voltage and current. These methods have inherent variations and need to be calibrated and the zero point needs to be set. This is generally done at the factory during assembly and sometimes adjusted by service personnel. Variables that impact the zero point may include ambient temperature, injector wear, line voltage, and manufacturing variations in the syringe.